1. Field of the Invention
The present invention relates to a Josephson junction coupled to a Schottky diode semiconductor, and to the use of such a three terminal device as a current amplifier.
2. Description of Prior Art
A somewhat similar device has been described by S. Sakai and H. Tateno, Electronics Letters 17, 501 (Jul. 9, 1981). Their three-terminal device involves a Nb thin-film microbridge on a silicon substrate. They saw a depression in the critical current, as we did, when current was injected from the semiconductor into the superconductor. The big difference between our devices is that they used a microbridge-type Josephson device. Such a device exhibits a critical current, but does not have a junction gap voltage. This means that the biasing arrangement we have used to get high current gains is not possible with their device.
A more similar device was discussed by Kobayashi, Miura, Tonouchi, and Fujisawa, IEEE Trans. on Magnetics 21, 924 (Mar. (1985). Their device involved a Nb tunnel junction on both a GaAs and an InP semiconductor substrate. The difference between our devices is that they did not see any change in either the junction critical current or the junction gap voltage when current was injected from the semiconductor into the base electrode of the Josephson junction. To get current amplification of any sort from the device they had to irradiate it with microwaves. The I-V curve of a Josephson junction changes in a characteristic way under microwave irradiation, and they observed that the "steps" were affected by a current across the Schottky barrier. Without external microwave irradiation, no current gain was observed.